/* -*-c++-*- */
/* osgEarth - Dynamic map generation toolkit for OpenSceneGraph
* Copyright 2008-2012 Pelican Mapping
* http://osgearth.org
*
* osgEarth is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with this program.  If not, see <http://www.gnu.org/licenses/>
*/

#ifndef OPTIONAL_HPP
#define OPTIONAL_HPP

namespace mp
{
	namespace xml
	{
		/**
		 * A template for defining "optional" class members. An optional member has a default value
		 * and a flag indicating whether the member is "set".
		 * This is used extensively in osgEarth's ConfigOptions subsystem.
		 */
		template<typename T> struct optional {
			optional() : _set(false), _value(T()), _defaultValue(T()) { }
			optional(T defaultValue) : _set(false), _value(defaultValue), _defaultValue(defaultValue) { }
			optional(T defaultValue, T value) : _set(true), _value(value), _defaultValue(defaultValue) { }
			optional(const optional<T>& rhs) { (*this)=rhs; }
			virtual ~optional() { }
			optional<T>& operator =(const optional<T>& rhs) { _set=rhs._set; _value=rhs._value; _defaultValue=rhs._defaultValue; return *this; }
			const T& operator =(const T& value) { _set=true; _value=value; return _value; }
			bool operator ==(const optional<T>& rhs) const { return _set && rhs._set && _value==rhs._value; }
			bool operator !=(const optional<T>& rhs) const { return !( (*this)==rhs); }
			bool operator ==(const T& value) const { return _value==value; }
			bool operator !=(const T& value) const { return _value!=value; }
			bool operator > (const T& value) const { return _value>value; }
			bool operator >=(const T& value) const { return _value>=value; }
			bool operator < (const T& value) const { return _value<value; }
			bool operator <=(const T& value) const { return _value<=value; }
			bool isSetTo(const T& value) const { return _set && _value==value; } // differs from == in that the value must be explicity set
			bool isSet() const { return _set; }
			void unset() { _set = false; _value=_defaultValue; }

			//T& get() { return _value; }
			const T& get() const { return _value; }
			const T& value() const { return _value; }
			const T& defaultValue() const { return _defaultValue; }
			T temp_copy() const { return _value; }

			// gets a mutable reference, automatically setting
			T& mutable_value() { _set = true; return _value; }

			void init(T defValue) { _value=defValue; _defaultValue=defValue; unset(); }

			operator const T*() const { return &_value; }

			T* operator ->() { _set=true; return &_value; }
			const T* operator ->() const { return &_value; }

		private:
			bool _set;
			T _value;
			T _defaultValue;
			typedef T* optional::*unspecified_bool_type;

		public:
			operator unspecified_bool_type() const { return 0; }
		};
	}
}
#endif // OPTIONAL_HPP
